904 kickdown

I have a 67 barracuda, that had a 273 with a 904. I put in a nice 340 and kept my 904. My problem is I went with the Lokar throttle and kickdown and now I can't get the kickdown to kickdown when floored. My tranny was rebuilt about a 1000 miles ago and ran very nice, shifted hard etc. When rebuilt, they put a shift kit in. Now it seems to shift early and not shift as hard, and like I said won't kick down. When I want to get on it, I just manually drop it down and it runs great. I have had a couple of people tell me that running it with no kickdown may damage the tranny and the wrong adjustment on the kickdown could be causing it to shift early and soft. I have driven it about 300 miles or so like this. Is this true?